Eurasian birds are invading North America, and it is having a negative effect on native species. According to a University of Tennessee at Knoxville study, warming climates allow various species to get closer to and even cross the Bering Strait--that natural barrier, roughly 50 miles wide, that connects the Pacific and Arctic oceans between Russia and Alaska.

Over the past 20 years, Vladimir Dinets, a research assistant professor of psychology, has seen dramatic changes in the Strait's landscape. He noted that what was once open tundra is now overgrown with shrubbery. According to a news release, many species are using this to their advantage.   

For this study, recently published in the Journal of Field Ornithology, the researchers observed two species of Eurasian cuckoos, of which one has already been seen breeding in North America. Another is packing up to join its relatives. This is bad news for native birds, since the Eurasian cuckoos are known for nest robbing and being "brood parasites"--which means that they throw out the host's eggs to lay their own, in order to reduce competition. This could cause drastic population declines for native birds unable to protect and ensure the growth and development of their offspring.

"It is important to predict which native species are most at risk and to monitor their populations so that if they start to decline catastrophically, we can establish captive breeding programs and other supportive measures," Dinets said in a statement.

While some birds have notably developed defense mechanisms against other brood parasites, such as cowbirds, the researchers don't think the same tactics will be successful for defending against Eurasian cuckoos. This is because cuckoos are sneakier parasites, in that they can mimic their host's egg color and apply other subterfuges, according to the statement.

The researchers suggest that western Alaska is where the cuckoos might start invading North America first, the release noted. They recommend that people learn how to identify Eurasian cuckoos, so that they can help mitigate the effects of their invasion. 

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